Why do SV's have engine braking?

Originally Posted by ophic

i'm saying that is exactly what happens in some engines - the engine effectively dies until either the throttle is opened again or the ECU detects it nearing tickover - when it will supply the appropriate idle mixture to prevent it cutting out. Whether this happens in the SV or not i have no idea. However this is getting way off the point.

not getting off point, trying to suck air thru a closed throttle is want makes engine braking,

Originally Posted by RandyO

engine braking is not caused by frictional losses, it's all pulling vaccum thru the intake

You must tell me the secret of this friction free engine, I'll retire next week!
Some of the braking effect is due to friction, some to pumping losses through the inlet/exhaust system and some to crankcase pumping. What we are trying to establish is the difference between the V twin and the IL4.
And it's not due to pumping against a vacuum. The more air you pump the more braking effect you will get. If the throttle slides closed completely you would have zero pumping losses.

My guess is that the SV has greater engine braking on the over-run for exactly the same reason it has more torque than an il4 when the throttle is open.

Question is, why has it got more torque?

Originally Posted by Tildo

My guess is that the SV has greater engine braking on the over-run for exactly the same reason it has more torque than an il4 when the throttle is open.

Question is, why has it got more torque?

cause the individual cylinders are bigger. each intake stroke has to suck 325cc of air thru a closed or partially closed throttle

It also has to compress the gases which to me explains the engine braking.
To tell you the truth, It should make little difference how many cylinders there are. The most engine braking i've ever had was on my 900cc 6 cylinder, It would lock up the wheel at any speed.

Originally Posted by Tildo

My guess is that the SV has greater engine braking on the over-run for exactly the same reason it has more torque than an il4 when the throttle is open.

Question is, why has it got more torque?

It's got more torque because the cam timing is optomised to produce more torque at low revs, it's got nothing to do with cylinder confiquration. It would be exaclly the same power characteristics as a parallel twin.

Originally Posted by Tildo

My guess is that the SV has greater engine braking on the over-run for exactly the same reason it has more torque than an il4 when the throttle is open.

Question is, why has it got more torque?

V-Twins don't have more torque than IL4s.

Originally Posted by Flamin_Squirrel

V-Twins don't have more torque than IL4s.

You beat me to it

Squirrel's post is B.A.S.A.T. Compliant.

[ophic]

and the answer is... they don't. I found an article comparing IL4s and V-twins. Will post a link when i find it again. It says a TL1000 has approx the same engine braking effect as a similar sporty IL4. Not entirely sure i believe this though.

Is the cross sectional area of the SV cylinder greater than the equivalent capacity IL4? If so, the same vacuum pressure in the empty pot will cause a larger force to be applied to the surface of the cylinder head.

Pressure = force / area